In a small saucepan, melt the butter and sauté the onion and oregano. Add the flour and toast it in the butter mixture until you have a lightly golden and bubbly roux. Pour in the broth or bean liquid, whisking constantly. When the mixture boils slightly and begins to thicken, add the tomato paste, salt and pepper.

You can add other seasonings at this point as it suits you. I added the chipotle pepper from my black bean burger recipe, plus I was using the cooking liquid from the beans, so my sauce had traces of cilantro, black bean, cumin, and epazote.

Allow the sauce to bubble, covered while you stuff the enchiladas. Check the sauce’s seasonings before you ladle it over the enchiladas, top with cheese, and bake until bubbly.